Superconducting compound quantum computing circuit

ABSTRACT

A superconducting complex quantum computing circuit includes a circuit substrate in which a wiring pattern of a circuit element including quantum bits and measurement electrodes, and ground patterns are formed, and through-electrodes connecting the ground pattern formed on a first surface of the substrate surface and the ground pattern formed on a second surface; a first ground electrode including a first contact portion in contact with the ground patterns, and a first non-contact portion having a shape corresponding to a shape of the wiring pattern; a second ground electrode including a second contact portion in contact with the ground pattern; a control signal line provided with a contact spring pin at a tip; and a pressing member that presses the first ground electrode against the first surface of the circuit substrate or presses the second ground electrode against the second surface of the circuit substrate.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims priority to Japanese Patent Application No.2018-191287, filed on Oct. 9, 2018, the content of which is incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates to a superconducting complex quantumcomputing circuit.

BACKGROUND OF THE INVENTION

Research and development for a technology related to a quantum computerare being performed. In the technology related to the quantum computer,a method for performing a two-quantum bit gate operation in the quantumcomputer using a superconducting quantum bit is known (see PatentDocuments 1 and 2).

CITATION LIST

Patent Document 1: U.S. Pat. No. 7,613,765.

Patent Document 2: U.S. Patent Application Publication No. 2016/0380636.SUMMARY OF THE INVENTION Technical Problem

A quantum circuit according to the related art, which is developed forrealization of a quantum computer using a superconducting circuit, has acircuit configuration in which it is difficult to completely turn off anunnecessary interaction between quantum bits required for operations. Ina case where there is a residual interaction when the interaction isturned off, an error generated in the quantum bits propagates tosurroundings and causes diffusion in addition to the residualinteraction itself causing a control error of the quantum bits. The factthat the residual interaction itself causes the control error of thequantum bits and that the error generated in the quantum bits propagatesand diffuses to the surroundings becomes a critical issue inimplementation of the quantum computer having error tolerance, and atthe same time, becomes a critical issue that leads to a decrease incomputational accuracy and precision of approximated computation withouthaving the error tolerance.

The present invention has been made in view of the above issues, andprovides a superconducting complex quantum computing circuit which cansuppress the interaction and the crosstalk among the quantum bits.

Solution to Problem

The present invention has been made to solve the above-mentionedproblem, and according to one aspect of the present invention, there isprovided a superconducting complex quantum computing circuit including:a circuit substrate in which a wiring pattern of a circuit element,which includes a quantum bit and a measurement electrode for observing astate of the quantum bit, and a ground pattern which is at a groundpotential are formed on the substrate surface, and that includes athrough-substrate electrode which connects the ground pattern formed ona first surface of the substrate surface and the ground pattern formedon a second surface, which is a surface opposite the first surface,inside the substrate; first ground electrodes that include a firstcontact portion which is in contact with the ground pattern formed onthe first surface of the circuit substrate, and a first non-contactportion which has a shape corresponding to a shape of the wiring patternformed on the first surface; a second ground electrode that includes asecond contact portion which is in contact with the ground patternformed on the second surface of the circuit substrate; a control signalline that is provided with a contact spring pin at a tip, the pin beingin contact with a position corresponding to the quantum bit to press thefirst surface of the circuit substrate against the first groundelectrode or to press the second surface of the circuit substrateagainst the second ground electrode; and a pressing member that pressesthe first ground electrode against the first surface of the circuitsubstrate or presses the second ground electrode against the secondsurface of the circuit substrate, in which the first ground electrode isin contact with the ground pattern via a first extension portion formedby a superconductor having extensibility higher than extensibility ofthe ground pattern, and the second ground electrode is in contact withthe ground pattern via a second extension portion formed by asuperconductor having extensibility higher than the extensibility of theground pattern.

Further, according to one aspect of the present invention, thesuperconducting complex quantum computing circuit further includes thepressing member that presses the first ground electrode against thefirst surface of the circuit substrate or presses the second groundelectrode against the second surface of the circuit substrate, in whichthe first ground electrode is in contact with the ground pattern via afirst extension portion formed by a superconductor having extensibilityhigher than the extensibility of the ground pattern, and the secondground electrode is in contact with the ground pattern via a secondextension portion formed by a superconductor having extensibility higherthan the extensibility of the ground pattern.

Further, according to one aspect of the present invention, in thesuperconducting complex quantum computing circuit, the quantum bitincludes a first electrode that has a first coupling capacitance with aground portion, and a second electrode that has a second couplingcapacitance with a ground portion larger than the first couplingcapacitance and that is connected to the first electrode by a Josephsonjunction.

Further, according to one aspect of the present invention, in thesuperconducting complex quantum computing circuit, the circuit substrateincludes, at a quantum bit correspondence position, which is a positionof the second surface, corresponding to a position of the quantum bitincluded in the wiring pattern formed on the first surface, a centralelectrode, a surrounding electrode that surrounds the surroundings ofthe central electrode, and a connection electrode that connects thecentral electrode and the surrounding electrode.

Further, according to one aspect of the present invention, in thesuperconducting complex quantum computing circuit, a control signal lineis further included that supplies a control signal to the quantum bitand that is arranged inside the first non-contact portion included inthe first ground electrode at a position corresponding to a position ofthe quantum bit included in the wiring pattern formed on the firstsurface or inside a second non-contact portion included in the secondground electrode at a position corresponding to a quantum bitcorrespondence position, which is a position of the second surfacecorresponding to the position of the quantum bit included in the wiringpattern formed on the first surface.

Further, according to one aspect of the present invention, in thesuperconducting complex quantum computing circuit, the first non-contactportion and the second non-contact portion have a width and a heightwith sizes smaller than a wavelength of the control signal.

Further, according to one aspect of the present invention, in theabove-mentioned superconducting complex quantum computing circuit, afrequency band of the control signal is a microwave band.

Advantageous Effects of the Invention

According to the present invention, it is possible to suppressinteraction and crosstalk between quantum bits.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing an example of a configuration of asuperconducting complex quantum computing circuit according to anembodiment of the present invention.

FIG. 2 is a top view of an observation area of a substrate surfaceaccording to the embodiment of the present invention.

FIG. 3 is a diagram showing an example of a first non-contact portionand a first contact portion according to the embodiment of the presentinvention.

FIG. 4 is a diagram showing an example of a quantum bit according to theembodiment of the present invention.

FIG. 5 is a diagram showing an example of a first equivalent circuitaccording to the embodiment of the present invention.

FIG. 6 is a diagram showing an example of a filter pattern according tothe embodiment of the present invention.

FIG. 7 is a diagram showing an example of a second equivalent circuitaccording to the embodiment of the present invention.

FIG. 8 is a diagram showing an example of a relationship of a currentflowing through a third capacitor according to the embodiment of thepresent invention with respect to a frequency of a control current.

FIG. 9 is a diagram showing an example of a cross section of a part ofthe quantum bit of the superconducting complex quantum computing circuitaccording to the embodiment of the present invention.

FIG. 10 is a diagram showing an example of a superconducting resonatorand an observation electrode according to the embodiment of the presentinvention.

FIG. 11 is a diagram showing an example of a cross section of a part ofthe observation electrode of the superconducting complex quantumcomputing circuit according to the embodiment of the present invention.

FIG. 12 is a diagram showing an example of a quantum bit according to amodified example of the present invention.

FIG. 13 is a diagram showing an example of the quantum bit according tothe modified example of the present invention.

FIG. 14 is a diagram showing an example of the quantum bit according tothe modified example of the present invention.

FIG. 15 is a diagram showing an example of the quantum bit according tothe modified example of the present invention.

FIG. 16 is a diagram showing an example of the quantum bit according tothe modified example of the present invention.

FIG. 17 is a diagram showing an example of the quantum bit according tothe modified example of the present invention.

FIG. 18 is a diagram showing an example of the quantum bit according tothe modified example of the present invention.

FIG. 19 is a diagram showing an example of a filter pattern according tothe modified example of the present invention.

FIG. 20 is a diagram showing an example of the filter pattern accordingto the modified example of the present invention.

FIG. 21 is a diagram showing an example of the filter pattern accordingto the modified example of the present invention.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. FIG. 1 is a diagramshowing an example of a configuration of a superconducting complexquantum computing circuit QC according to the present embodiment. Thesuperconducting complex quantum computing circuit QC includes a circuitsubstrate 1, a first ground electrode 2, and a second ground electrode3. The circuit substrate 1 is sandwiched between the first groundelectrode 2 and the second ground electrode 3.

A side where the first ground electrode 2 is provided is referred to asan upper side when viewed from the circuit substrate 1, and a side wherethe second ground electrode 3 is provided is referred to as a lower sidewhen viewed from the circuit substrate 1.

The circuit substrate 1 is, for example, a dielectric substrate such assilicon. In the circuit substrate 1, a wiring pattern CP of a circuitelement and a ground pattern GP are formed by a superconducting film ona substrate surface S of the dielectric substrate such as silicon. In acase where a material of the circuit substrate 1 is silicon, the circuitsubstrate 1 is provided at a temperature lower than a predeterminedtemperature, and the silicon is a dielectric.

The wiring pattern CP includes a quantum bit 4, an observation electrode8 for observing a state of the quantum bit 4, a superconductingresonator 7, and a capacitor 9. In FIG. 1, as an example of the quantumbit 4, quantum bits 4-1 to 4-6 are shown. In FIG. 1, as an example ofthe superconducting resonator 7, superconducting resonators 7-1 to 7-4are shown. In FIG. 1, as an example of the capacitor 9, capacitors 9-1to 9-4 are shown.

The ground pattern GP is at a ground potential. The ground pattern GPincludes a first ground pattern GP1 and a second ground pattern GP2. Thefirst ground pattern GP1 is formed on a first surface S1 on the upperside of the substrate surface S. A second ground pattern GP2 is formedon a second surface S2 which is a surface opposite the first surface S1.The first ground pattern GP1 includes a substrate top surface groundelectrode 11. In FIG. 1, as an example of the substrate top surfaceground electrode 11, substrate top surface ground electrodes 11-1 to11-4 are shown.

A through-electrode 10 connects the first ground pattern GP1 formed onthe first surface S1 of the circuit substrate 1 to the second groundpattern GP2 formed on the second surface S2, which is the surfaceopposite the first surface S1, inside the substrate. The first groundpattern GP1 is in electrical contact with the second ground pattern GP2through the through-electrode 10. In FIG. 1, as an example of thethrough-electrode 10, a through-electrode 10-1 and a through-electrode10-2 are shown.

Further, a quadrangular area having four adjacent quantum bits 4, suchas quantum bits 4-1 to 4-4, as vertices on the substrate surface S ofthe circuit substrate 1 is referred to as an observation area X. In FIG.1, as an example of the observation area X, an observation area X1 andan observation area X2 are shown.

A quadrangular area having four adjacent quantum bits 4, such as thequantum bit 4-4, the quantum bit 4-3, a quantum bit 4-5, and a quantumbit 4-6, which are adjacent to each other, as vertices on the dielectricsubstrate of the circuit substrate 1 is referred to as a gap ground areaY. In FIG. 1, as an example of the gap ground area Y, a first gap groundarea Y1 and a first gap ground area Y2 are shown.

On the substrate surface S, a pattern having the observation area X andthe gap ground area Y surrounding the observation area X is repeated. InFIG. 1, a part of the pattern is shown.

As described above, in the circuit substrate 1, the wiring pattern CP ofthe circuit element, which includes the quantum bit 4 and theobservation electrode 8 for observing the state of the quantum bit 4,and the ground pattern GP, which is at the ground potential, are formedon the substrate surface S. The circuit substrate 1 includes thethrough-electrode 10 which connects the first ground pattern GP1 formedon the first surface S1 of the substrate surface S and the second groundpattern GP2 formed on the second surface S2, which is the surfaceopposite the first surface S1, inside the substrate.

The superconducting film is formed on the first ground electrode 2 afteran etching process is performed on a surface facing the substratesurface S in accordance with the wiring pattern CP on the substratesurface S. A first non-contact portion 20 is formed in the first groundelectrode 2 by the etching process.

The first non-contact portion 20 is not in contact with the firstsurface S1 of the substrate surface S. A distance between the firstnon-contact portion 20 and the first surface S1 is, for example, severaltens to several hundreds of microns in a case where a control signalfrequency is about 10 GHz. A width and a height of the first non-contactportion 20 (the same as a second non-contact portion 30) have sizessmaller than a wavelength of the control signal. The first non-contactportion 20 has a shape corresponding to a shape of the wiring pattern CPformed on the first surface S1 of the substrate surface S.

On the other hand, the first ground electrode 2 is provided with a firstcontact portion 21 as a part of the surface of the first groundelectrode 2 facing the substrate surface S other than the firstnon-contact portion 20.

The first contact portion 21 is in contact with the first ground patternGP1 formed on the first surface S1 of the circuit substrate 1 via a topsurface superconducting micro bump 12-1. The top surface superconductingmicro bump 12-1 is, for example, a superconductor having extensibilityhigher than extensibility of the ground pattern GP. The top surfacesuperconducting micro bump 12-1 is an example of a first extensionportion 12.

Here, in the present embodiment, the extensibility is a property ofmalleability or ductility, or both malleability and ductility. In FIG.1, as an example of the first contact portion 21, a first contactportion 21-1, a first contact portion 21-2, and a first contact portion21-3 are shown.

As described above, the first ground electrode 2 is in contact with theground pattern GP via the first extension portion 12 formed by thesuperconductor having the extensibility higher than the extensibility ofthe ground pattern GP.

Here, the first non-contact portion 20 and the first contact portion 21will be described with reference to FIGS. 2 and 3.

FIG. 2 is a top view of the observation area X1 of the substrate surfaceS according to the present embodiment.

In FIG. 2, as an example of the first non-contact portion 20, a firstnon-contact portion 20-3, a first non-contact portion 20-4, a firstnon-contact portion 20-5, and a first non-contact portion 20-6 areshown.

FIG. 3 is a diagram showing an example of the first non-contact portion20 and the first contact portion 21 according to the present embodiment.In FIG. 3, as an example of the first contact portion 21, first contactportions 21-1 to 21-12 are shown. The first non-contact portion 20 is aportion excluding the first contact portion 21, and is formed byperforming the etching process as described above. In FIG. 3, as anexample of the first non-contact portion 20, a first non-contact portion20-1 and a first non-contact portion 20-2 are shown.

As described above, the first ground electrode 2 includes the firstcontact portion 21 which is in contact with the first ground pattern GP1formed on the first surface S1 of the circuit substrate 1, and the firstnon-contact portion 20 which has a shape corresponding to the shape ofthe wiring pattern CP formed on the first surface S1.

Returning to FIG. 1, description of the superconducting complex quantumcomputing circuit QC is continued.

The quantum bit 4 is a superconducting quantum bit formed on asuperconducting thin film. Here, the quantum bit 4 will be describedwith reference to FIGS. 4 and 5.

FIG. 4 is a diagram showing an example of the quantum bit 4 according tothe present embodiment. The quantum bit 4 includes an inner disk 40, anouter ring 41, a Josephson junction 42, a quantum bit hand portion 43-1,and a quantum bit hand portion 43-2. Each of the inner disk 40, theouter ring 41, the quantum bit hand portion 43-1 and the quantum bithand portion 43-2 is a metal electrode.

The inner disk 40 and the outer ring 41 form concentric metalelectrodes. The inner disk 40 and the outer ring 41 are joined by theJosephson junction 42. The outer ring 41 is connected to the quantum bithand portion 43-1, the quantum bit hand portion 43-2, a quantum bit handportion 43-3, and a quantum bit hand portion 43-4. In FIG. 4, thequantum bit hand portion 43-3 and the quantum bit hand portion 43-4 arenot shown.

The surroundings of the outer ring 41 are surrounded by the substratetop surface ground electrode 11. The substrate top surface groundelectrode 11-1 and the substrate top surface ground electrode 11-2 areexamples of the substrate top surface ground electrode 11.

Here, a first equivalent circuit 4C, which is an equivalent circuit ofthe quantum bit 4, will be described with reference to FIG. 5.

FIG. 5 is a diagram showing an example of the first equivalent circuit4C according to the present embodiment. A capacitor Cdq is formedbetween the inner disk 40 and the outer ring 41 which are the concentricmetal electrodes. In the first equivalent circuit 4C, a non-linear LCresonator LCR is formed by the capacitor Cdq and an inductor derivedfrom the Josephson junction 42. The capacitor Cdq has a capacitance Cq.

The first ground electrode 2, the second ground electrode 3, thesubstrate top surface ground electrode 11, and a substrate bottomsurface ground electrode 13 are collectively referred to as a groundportion GE.

A first capacitor Cd1 is formed between the inner disk 40 and the groundportion GE. The first capacitor Cd1 has a first capacitance C1. Thefirst capacitance C1 is mainly determined by a distance between theinner disk 40 and the substrate top surface ground electrode 11. In theexample of FIG. 4, the distance between the inner disk 40 and thesubstrate top surface ground electrode 11 is determined by a radius ofthe inner disk 40.

A second capacitor Cd2 is formed between the outer ring 41 and theground portion GE. The second capacitor Cd2 has a second capacitance C2.The second capacitance is mainly determined by a distance between theouter ring 41 and the substrate top surface ground electrode 11. Thedistance between the outer ring 41 and the substrate top surface groundelectrode 11 is determined by a radius of the outer ring 41.

An unnecessary radiation electric field E may be generated between thequantum bit 4 and the first ground electrode 2 or between the quantumbit 4 and the ground portion GE. An unnecessary radiation electric fieldE1 is an example of the unnecessary radiation electric field E betweenthe quantum bit 4 and the ground portion GE. An unnecessary radiationelectric field E2 is an example of the unnecessary radiation electricfield E between the quantum bit 4 and the ground portion GE.

In the quantum bit 4, the radius of the inner disk 40 and the radius ofthe outer ring 41 are determined based on a condition that the secondcapacitance C2 is larger than the first capacitance C1. In the quantumbit 4, the radius of the outer ring 41 is increased so that the secondcapacitance C2 is larger than the first capacitance C1.

In the quantum bit 4, since the second capacitance C2 is larger than thefirst capacitance C1, fluctuation of a potential due to the unnecessaryradiation electric field E is propagated to the ground portion GE viathe outer ring 41. That is, the second capacitor Cd2 functions as aso-called bypass condenser.

Since the fluctuation of the potential due to the unnecessary radiationelectric field E is propagated to the ground portion GE via the outerring 41, a potential difference between the inner disk 40 and the outerring 41 is hardly affected by the fluctuation of the potential due tothe unnecessary radiation electric field E, compared to a case where thesecond capacitance C2 is not larger than the first capacitance C1. Here,it is necessary that the potential difference between the inner disk 40and the outer ring 41 be stable with respect to the unnecessaryradiation electric field E so that the quantum bit 4 functions as anelement for recording bit information.

As described above, the quantum bit 4 includes the inner disk 40 whichhas the first capacitance C1 with the ground portion GE, and the outerring 41 which has the second capacitance C2 with the ground portion GElarger than the first capacitance C1, and which is connected to theinner disk 40 by the Josephson junction 42.

Returning to FIG. 1, description of the configuration of thesuperconducting complex quantum computing circuit QC is continued.

The second ground electrode 3 is an aluminum electrode, as an example.The second ground electrode 3 includes the second non-contact portion 30and a second contact portion 31.

The second non-contact portion 30 is not in contact with the secondsurface S2 which is a surface on a lower side of the substrate surface Sof the circuit substrate 1. The second ground electrode 3 includes thesecond non-contact portion 30 at a position corresponding to a quantumbit correspondence position. Here, a quantum bit correspondence positionis a position of the second surface S2 corresponding to the position ofthe quantum bit 4 included in the wiring pattern CP formed on the firstsurface S1 which is a surface on an upper side of the substrate surfaceS of the circuit substrate 1. In FIG. 1, as an example of the secondnon-contact portion 30, a second non-contact portion 30-1 and a secondnon-contact portion 30-2 are shown.

The second contact portion 31 is in contact with the second groundpattern GP2 formed on the second surface S2 via a second extensionportion 14. Here, the second extension portion 14 is a superconductorsuch as indium having extensibility higher than the extensibility of theground pattern GP. The second extension portion 14 includes a conductivecontact portion 14-1 and a conductive contact portion 14-2, which willbe described later.

That is, the second ground electrode 3 is in contact with the groundpattern GP via the second extension portion 14 formed by thesuperconductor having extensibility higher than the extensibility of theground pattern GP.

In the second non-contact portion 30, a control signal line 5 isarranged to extend in a direction perpendicular to the second surface S2from the lower side. The control signal line 5 has two types including acontrol signal line 5A and an observation signal line 5B. The controlsignal line 5A is the control signal line 5 for transmitting a controlsignal to the quantum bit 4.

The observation signal line 5B is the control signal line 5 for fetchingan observation result of the state of the quantum bit 4 as a signal(referred to as an observation signal). The observation signal isgenerated by reflecting the observation result of the state of thequantum bit 4 by transmitting a probe signal through the observationsignal line 5B and reflecting the probe signal on the second surface S2of the observation electrode 8.

Microwaves in a 4 to 12 gigahertz band are usually used as the controlsignal and the observation signal, as an example. That is, in thesuperconducting complex quantum computing circuit QC, a frequency bandof the control signal is the microwave band.

A control current, which is the control signal of the quantum bit, ispropagated to the control signal line 5A and flows into a filter pattern6 formed on the substrate bottom surface ground electrode 13 by acontact spring pin 50A which is provided at a tip of the control signalline 5A. The control current flowing into the filter pattern 6 formed onthe second surface S2, which is a surface on a lower side of the circuitsubstrate 1, is circulated to the substrate bottom surface groundelectrode 13 after passing through several thin wires from the filterpattern 6 formed on the second surface S2.

As described above, the second ground electrode 3 includes the secondcontact portion 31 which is in contact with the second ground patternGP2 formed on the second surface S2 of the circuit substrate 1.

Further, the control signal line 5 is arranged inside the secondnon-contact portion 30 included in the second ground electrode 3 at aposition corresponding to the quantum bit correspondence position, whichis the position of the second surface S2 corresponding to the positionof the quantum bit 4 included in the wiring pattern CP formed on thefirst surface S1, and supplies the control signal to the quantum bit 4.The control signal line 5 is arranged in a direction perpendicular tothe substrate surface S of the circuit substrate 1 on which the quantumbit 4 is arranged. That is, the control signal line 5 is arranged basedon a three-dimensional structure.

Here, the filter pattern 6 will be described with reference to FIGS. 6and 7.

FIG. 6 is a diagram showing an example of the filter pattern 6 accordingto the present embodiment. The filter pattern 6 is provided at thequantum bit correspondence position which is the position of the secondsurface S2 corresponding to the position of the quantum bit 4. Thefilter pattern 6 includes a central electrode 60 and a connectionelectrode 62. The central electrode 60 is a circular electrode. Thecentral electrode 60 is surrounded by the substrate bottom surfaceground electrode 13 via a gap portion 61. The central electrode 60 andthe substrate bottom surface ground electrode 13 are connected via theconnection electrode 62. Here, the connection electrode 62 is a thinwire-shaped metal electrode having a width of several tens ofmicrometers.

In FIG. 6, gap portions 61-1 to 61-4 are examples of the gap portion 61.In FIG. 6, connection electrodes 62-1 to 62-4 are examples of theconnection electrode 62.

Here, a second equivalent circuit 4Ca, which is an equivalent circuit ofthe quantum bit 4 in a case where the filter pattern 6 is included, willbe described with reference to FIG. 7.

FIG. 7 is a diagram showing an example of the second equivalent circuit4Ca according to the present embodiment. In a case where the secondequivalent circuit 4Ca (FIG. 7) is compared with the first equivalentcircuit 4C (FIG. 5), the control signal line 5A, an inductor Ids, and athird capacitor Cdc are different, and functions of other components(the first capacitor Cd1, the second capacitor Cd2, the LC resonatorLCR, the inner disk 40, the outer ring 41, the quantum bit hand portion43-1, the quantum bit hand portion 43-2, and the ground portion GE) arethe same. In FIG. 7, parts which are different from the first equivalentcircuit 4C in FIG. 5 will be mainly described.

The third capacitor Cdc is formed between the control signal line 5A andthe inner disk 40. The third capacitor Cdc has a third capacitance Cc.

The connection electrode 62 forms the inductor Ids provided in parallelwith the third capacitor Cdc. The inductor Ids connects the controlsignal line 5A and the ground portion GE. The inductor Ids has aninductance Ls.

A drive electric field ED is an electric field generated by the controlcurrent flowing through the control signal line 5A.

The inductor Ids, the third capacitance Cc, the first capacitor Cd1, andthe second capacitor Cd2 form a high-pass filter. Here, since the secondcapacitance C2 of the second capacitor Cd2 is sufficiently larger thanthe first capacitance C1 of the first capacitor Cd1, the secondcapacitor Cd2 almost has an effect, compared to an effect of the firstcapacitor Cd1, on the first capacitor Cd1 and the second capacitor Cd2of the high-pass filter. The high-pass filter passes a signal at afrequency sufficiently higher than the microwave band to the outside ofthe control signal line 5A or the like. As described above, themicrowaves are used as the control signal of the quantum bit 4. Theinductor Ids suppresses energy of the quantum bit 4 from leaking to theoutside.

Here, an effect of the connection electrode 62, which is the inductorIds, will be described.

The control current supplied from the control signal line 5A is definedas a control current I, a current component of the control current Iflowing to a side of the third capacitor Cdc is defined as a current Ic,and a current component of the control current I flowing to a side ofthe inductor Ids is defined as a current IL. A magnitude of the controlcurrent I is defined as a magnitude i, a magnitude of the current Ic isdefined as a magnitude iC, and a magnitude of the current IL is definedas a magnitude iL.

In a case where the inductance Ls of the inductor Ids is infinite, themagnitude iL of the current IL becomes zero, and the magnitude iC of thecurrent Ic becomes equal to the magnitude i of the control current I. Ina case where the LC resonator LCR resonates, a magnitude of a parallelimpedance becomes zero.

The current flowing through the LC resonator LCR is the currentcomponent that flows to a side of the second capacitor Cd2 of thecurrent component of the current Ic that flows to a side of the firstcapacitor Cd1 and the current component that flows to the side of thesecond capacitor Cd2. A magnitude of the current flowing through the LCresonator LCR is represented as in Equation (1).

$\begin{matrix}{{\frac{\frac{1}{C_{1}}}{\frac{1}{C_{1}} + \frac{1}{C_{2}}}i_{c}} = {\frac{C_{2}}{C_{1} + C_{2}}i_{c}}} & (1)\end{matrix}$

In a case where the inductance Ls becomes small, the magnitude iL of thecurrent IL increases and the magnitude iC of the current Ic decreases.Therefore, according to the above Equation (1), in a case where theinductance Ls becomes small, the magnitude of the current flowingthrough the LC resonator LCR decreases.

Here, the magnitude i of the control current I is represented as inEquation (2).

$\begin{matrix}{i = {\frac{\left( {\frac{1}{j\;{\omega\left( {C_{1} + C_{2}} \right)}} + \frac{1}{j\;\omega\; C_{C}}} \right)j\omega L_{S}}{\frac{1}{j{\omega\left( {C_{1} + C_{2}} \right)}} + \frac{1}{j\;\omega\; C_{C}} + {j\;\omega\; L_{S}}}V}} & (2)\end{matrix}$

In a case where the second capacitance C2 is sufficiently larger thanthe third capacitance Cc, the magnitude i of the control current I isrepresented as in Equation (3) based on Equation (2).

$\begin{matrix}{{i\overset{C_{2}\operatorname{>>}\; C_{C}}{\longrightarrow}\frac{\frac{L_{S}}{C_{C}}}{\frac{1}{j\;\omega\; C_{C}} + {j\omega L_{S}}}}V} & (3)\end{matrix}$

In a case where the second capacitance C2 is sufficiently larger thanthe third capacitance Cc, the magnitude iC of the current Ic isrepresented as in Equation (4) based on Equation (3).

$\begin{matrix}{{i_{C}\overset{C_{2}\operatorname{>>}\; C_{C}}{\longrightarrow}\frac{j\;\omega\; L_{S}}{\frac{1}{j\;\omega\; C_{C}} + {j\;\omega\; L_{S}}}}{{\cdot i} = {{\frac{j\omega\frac{L_{S}^{2}}{C_{C}}}{\left( {\frac{1}{j\;\omega\; C_{C}} + {j\;\omega\; L_{S}}} \right)^{2}} \cdot V} = \frac{\frac{1}{j\;\omega\; C_{C}} \cdot V}{\left( {1 - \left( {\omega^{2}LC_{C}} \right)^{- 1}} \right)^{2}}}}} & (4)\end{matrix}$

Here, a relationship between the control current I of the current Icflowing through the third capacitor Cdc with respect to a frequency ωwill be described with reference to FIG. 8.

FIG. 8 is a diagram showing an example of the relationship between thecontrol current I of the current Ic flowing through the third capacitorCdc with respect to the frequency ω according to the present embodiment.A graph G1 shows a logarithm of the magnitude iC of the current Ic withrespect to a logarithm of the frequency ω of the control current I.Here, on a horizontal axis of the graph G1, the frequency ω of thecontrol current I is standardized by a resonance frequency of the LCresonator of the inductor Ids and the third capacitor Cdc.

Here, the resonance frequency of the LC resonator LCR is represented inEquation (5).

$\begin{matrix}{\frac{1}{2\;\pi}\frac{1}{\sqrt{\left( {C_{q} + C_{1}} \right)}L_{S}}} & (5)\end{matrix}$

The resonance frequency, which is in the microwave band, of the LCresonator LCR corresponds to a value included in a range X in thevicinity of a value of 0.1 on the coordinate of the horizontal axis.Since the frequency ω of the control current I is in the microwave band,the inductor Ids does not pass frequencies lower than the range X, andfunctions as the high-pass filter.

As described above, the circuit substrate 1 includes, at the quantum bitcorrespondence position, which is the position of the second surface S2corresponding to the position of the quantum bit 4 included in the firstground pattern GP1 formed on the first surface S1, the central electrode60, the substrate bottom surface ground electrode 13 which surrounds thesurroundings of the central electrode 60, and the connection electrode62 which connects the central electrode 60 and the substrate bottomsurface ground electrode 13.

Here, a cross section of a part of the quantum bit 4 of thesuperconducting complex quantum computing circuit QC will be describedwith reference to FIG. 9.

FIG. 9 is a diagram showing an example of the cross section of the partof the quantum bit 4 of the superconducting complex quantum computingcircuit QC according to the present embodiment.

The control signal line 5A includes the contact spring pin 50A and acoaxial wire dielectric portion 52A. The contact spring pin 50A includesa spring 51A inside, and presses the circuit substrate 1 against thefirst ground electrode 2 by elastic force of the spring 51A. The coaxialwire dielectric portion 52A insulates the contact spring pin 50A fromthe second ground electrode 3. A shape of the coaxial wire dielectricportion 52A is a cylindrical shape. FIG. 9 shows, as an example of across section of the coaxial wire dielectric portion 52A, a coaxial wiredielectric portion 52A-1 and a coaxial wire dielectric portion 52A-2.

The conductive contact portion 14-1 is provided between the substratebottom surface ground electrode 13-1 and a second contact portion 31-1.The conductive contact portion 14-2 is provided between a substratebottom surface ground electrode 13-2 and a second contact portion 31-2.As described above, the conductive contact portion 14-1 and theconductive contact portion 14-2 are examples of the second extensionportion 14.

The superconducting micro bump may be provided instead of the conductivecontact portion 14-1 and the conductive contact portion 14-2.

Here, the superconducting complex quantum computing circuit QC includesa pressing member P (not shown), which presses the first groundelectrode 2 against the first surface S1 of the circuit substrate 1, onan upper side of the first ground electrode 2. Here, the pressing memberP presses the first ground electrode 2 against the first surface S1 ofthe circuit substrate 1 in a direction opposite to the elastic force ofthe spring 51A.

The pressing member P presses the first ground electrode 2 against thefirst surface S1 of the circuit substrate 1, thereby causing the firstground electrode 2 to be adhered to the circuit substrate 1 and causingthe circuit substrate 1 to be adhered to the second ground electrode 3.The pressing member P is a leaf spring or a contact spring pin, as anexample.

With this configuration, the substrate bottom surface ground electrode13-1 and the substrate bottom surface ground electrode 13-2 are adheredto the second ground electrode 3, and the potentials thereof areequalized with the potential of the ground portion GE. As a result,since the potential of the outer ring 41 is effectively the same as thatof the ground portion GE via the second capacitance C2, it is possibleto cause the control signal to the quantum bit to reach the inner disk40 and the Josephson junction 42 that form the quantum bit with almostno leakage or crosstalk.

Returning to FIG. 1, description of the superconducting complex quantumcomputing circuit QC is continued.

The superconducting resonator 7 reads out the state of the quantum bit 4by interacting with the quantum bit 4. The four adjacent superconductingresonators 7-1 to 7-4 are aggregated by the observation electrode 8. Asdescribed above, the read state of the quantum bit 4 is fetched as theobservation signal to the observation signal line 5B via the observationelectrode 8.

Here, the superconducting resonator 7 and the observation electrode 8will be described with reference to FIGS. 10 and 11.

FIG. 10 is a diagram showing an example of the superconducting resonator7 and the observation electrode 8 according to the present embodiment.The superconducting resonator 7 has a meandering shape on the firstsurface S1, as an example. The shape of the superconducting resonator 7may be any shape as long as the superconducting resonator 7 functions asthe resonator. For example, the superconducting resonator 7 may have astraight linear shape or a U-shaped curved shape instead of themeandering shape.

The observation electrode 8 includes an observation substratethrough-electrode 80. The observation substrate through-electrode 80 hasthe same characteristics as the through-electrode 10 except that theobservation substrate through-electrode 80 is provided at a differentplace in the circuit substrate 1.

FIG. 11 is a diagram showing an example of a cross section of a part ofthe observation electrode 8 of the superconducting complex quantumcomputing circuit QC according to the present embodiment. A shape of theobservation substrate through-electrode 80 is a cylindrical shape. FIG.11 shows, as an example of the cross section of the observationsubstrate through-electrode 80, an observation substratethrough-electrode 80-1 and an observation substrate through-electrode80-2.

The observation signal line 5B includes a contact spring pin 50B and acoaxial wire dielectric portion 52B. The contact spring pin 50B includesthe spring 51B inside, and presses the circuit substrate 1 against thefirst ground electrode 2 by elastic force of the spring 51B. The coaxialwire dielectric portion 52B insulates the contact spring pin 50B fromthe second ground electrode 3. A shape of the coaxial wire dielectricportion 52B is a cylindrical shape. FIG. 11 shows, as an example of thecross section of the coaxial wire dielectric portion 52B, a coaxial wiredielectric portion 52B-1 and a coaxial wire dielectric portion 52B-2.

In the present embodiment, a case is described in which the controlsignal line 5 is arranged to extend from the inside of the secondnon-contact portion 30 included in the second ground electrode 3 in thedirection perpendicular to the second surface S2 of the substratesurface S from the lower side. However, the present embodiment is notlimited thereto. The control signal line 5 may be arranged to extendfrom the inside of the first non-contact portion 20 included in thefirst ground electrode 2 in a direction perpendicular to the firstsurface S1 of the substrate surface S from an upper side.

That is, the control signal line 5 may be arranged inside the firstnon-contact portion 20 included in the first ground electrode 2 at aposition corresponding to the position of the quantum bit 4 included inthe wiring pattern CP formed on the first surface S1.

In a case where the control signal line 5 is arranged to extend from theinside of the first non-contact portion 20 included in the first groundelectrode 2 in the direction perpendicular to the first surface S1 ofthe substrate surface S from the upper side, the filter pattern 6 maynot be provided in the superconducting complex quantum computing circuitQC.

Further, there may be a case where, for each quantum bit 4 and theobservation electrode 8, the control signal line 5 is arranged to extendfrom the inside of the second non-contact portion 30 included in thesecond ground electrode 3 in the direction perpendicular to the secondsurface S2 of the substrate surface S from the lower side, and a casewhere the control signal line 5 is arranged to extend from the inside ofthe first non-contact portion 20 included in the first ground electrode2 in the direction perpendicular to the first surface S1 of thesubstrate surface S from the upper side.

Note that, in the present embodiment, the case where the pressing memberP presses the first ground electrode 2 against the first surface S1 ofthe circuit substrate 1 is described. However, the present embodiment isnot limited thereto. The pressing member P may press the second groundelectrode 3 against the second surface S2 of the circuit substrate 1.Further, the superconducting complex quantum computing circuit QC mayinclude two types of pressing members, that is, a pressing member thatpresses the first ground electrode 2 against the first surface S1 of thecircuit substrate 1, and a pressing member that presses the secondground electrode 3 against the second surface S2 of the circuitsubstrate 1.

As described above, the superconducting complex quantum computingcircuit QC according to the present embodiment includes the circuitsubstrate 1, the first ground electrode 2, and the second groundelectrode 3.

In the circuit substrate 1 the wiring pattern CP of the circuit element,which includes the quantum bit 4 and the observation electrode 8 forobserving the state of the quantum bit 4, and the ground pattern GPwhich is at the ground potential are formed on the substrate surface S,and the circuit substrate 1 includes the through-electrode 10 whichconnects the first ground pattern GP1 formed on the first surface S1 ofthe substrate surface S and the second ground pattern GP2 formed on thesecond surface S2, which is the surface opposite the first surface S1,inside the substrate.

The first ground electrode 2 includes the first contact portion 21 whichis in contact with the first ground pattern GP1 formed on the firstsurface S1 of the circuit substrate 1, and the first non-contact portion20 which has a shape corresponding to the shape of the wiring pattern CPformed on the first surface S1.

The second ground electrode 3 includes the second contact portion 31which is in contact with the second ground pattern GP2 formed on thesecond surface S2 of the circuit substrate 1.

With this configuration, in the superconducting complex quantumcomputing circuit QC according to the present embodiment, it is possibleto suppress the generation and extension of the unnecessaryelectromagnetic mode (a resonance phenomenon of electromagnetic waves)in a space on an upper side of the quantum bit 4 or in the circuitsubstrate 1, and thus interaction or crosstalk between the quantum bitscan be suppressed.

In the superconducting complex quantum computing circuit QC, the firstground electrode 2 causes the space on the upper side of the quantum bit4 to be small, compared to a case where the first ground electrode 2 isnot provided. The unnecessary electromagnetic mode may occur in thespace on the upper side of the quantum bit 4. In the superconductingcomplex quantum computing circuit QC, a mode frequency of theunnecessary electromagnetic mode can be detuned from the frequency ofthe quantum bit 4. Further, in the superconducting complex quantumcomputing circuit QC, the extension of the unnecessary electromagneticmode in the space on the upper side of the quantum bit 4 is localized,and thus it is possible to suppress crosstalk of the control signal ofthe quantum bit 4 over a wide range.

The through-electrode 10 can suppress the generation of the unnecessaryelectromagnetic mode in the circuit substrate 1 and can suppress thecrosstalk of the control signal between the quantum bits 4 over the widerange.

Further, the superconducting complex quantum computing circuit QCaccording to the present embodiment further includes the pressing memberP that presses the first ground electrode 2 against the first surface S1of the circuit substrate 1, or presses the second ground electrode 3against the second surface S2 of the circuit substrate 1.

Here, the first ground electrode 2 is in contact with the ground patternGP via the first extension portion 12 formed by the superconductorhaving the extensibility higher than the extensibility of the groundpattern GP.

The second ground electrode 3 is in contact with the ground pattern GPvia the second extension portion 14 formed by the superconducting bodieshaving the extensibility higher than the extensibility of the groundpattern GP.

With this configuration, in the superconducting complex quantumcomputing circuit QC according to the present embodiment, it is possibleto remove a gap between the first ground electrode 2 and the groundpattern GP on the first surface S1 of the circuit substrate 1 or a gapbetween the second ground electrode 3 and the ground pattern GP on thesecond surface S2 of the circuit substrate 1, and thus it is possible tosuppress crosstalk with both the control signal and the observationsignal which are propagated to the adjacent control signal line 5.

Further, in the superconducting complex quantum computing circuit QCaccording to the present embodiment, the quantum bit 4 includes a firstelectrode (in the example, the inner disk 40) which has a first couplingcapacitance (in the example, the first capacitance C1) with the groundportion GE, and a second electrode (in the example, the outer ring 41)which has a second coupling capacitance (in the example, the secondcapacitance C2) with the ground portion GE larger than the firstcoupling capacitance (in the example, first capacitance C1) and which isconnected to the first electrode (in the example, the inner disk 40) bythe Josephson junction 42.

With this configuration, in the superconducting complex quantumcomputing circuit QC according to the present embodiment, shielding fromthe unnecessary electromagnetic mode, which propagates through the metalelectrode (in the example, the inner disk 40 and the outer ring 41)constituting the quantum bit 4, is possible with the outer ring 41, andthus it is possible to suppress an error rate of the quantum bit 4.Here, the unnecessary electromagnetic mode, which propagates through themetal electrode (in the example, the inner disk 40 and the outer ring41) constituting the quantum bit 4, is, for example, an unnecessaryelectromagnetic mode that remains even though the first ground electrode2, the through-electrode 10, and the like are included.

In the related art, two metal electrodes forming the quantum bit aresymmetrical with respect to the ground electrode, or the metal electrodeon one side is grounded. A case where the two metal electrodes aresymmetrical with respect to the ground electrode is a case where acoupling capacitance between one metal electrode of the two metalelectrodes and the ground electrode is equal to a coupling capacitancebetween the other metal electrode of the two metal electrodes and theground electrode. Further, in a case where the metal electrode on oneside of the two metal electrodes forming the quantum bit is grounded isa case where the metal electrode on one side has an equivalent functionas the ground electrode.

In the superconducting complex quantum computing circuit QC according tothe present embodiment, it is possible to eliminate an influence ofpotential fluctuation of a ground electrode surface by notshort-circuiting the metal electrode on one side of the two metalelectrodes forming the quantum bit to the ground electrode.

Further, in the superconducting complex quantum computing circuit QCaccording to the present embodiment, the circuit substrate 1 includes,at the quantum bit correspondence position, which is the position of thesecond surface S2 corresponding to the position of the quantum bit 4included in the first ground pattern GP1 formed on the first surface S1,the central electrode 60, a surrounding electrode that surrounds thesurroundings of central electrode 60 (in the example, the substratebottom surface ground electrode 13), and the connection electrode 62which connects the central electrode 60 and the surrounding electrode(in the example, the substrate bottom surface ground electrode 13).

With this configuration, in the superconducting complex quantumcomputing circuit QC according to the present embodiment, in a casewhere the control of the quantum bit 4 is off, it is possible tosuppress leakage of the energy of the quantum bit 4 to the outside dueto the interaction between the quantum bit 4 and the control signal line5. Therefore, it is possible to suppress an error rate of calculation ofthe quantum bit 4.

Further, the superconducting complex quantum computing circuit QCaccording to the present embodiment further includes the control signalline 5. The control signal line 5 is arranged inside the firstnon-contact portion 20 included in the first ground electrode 2 in theposition corresponding to the position of the quantum bit 4 included inthe wiring pattern CP formed on the first surface S1, or inside of thesecond non-contact portion included in the second ground electrode 3 atthe position corresponding to the quantum bit correspondence position,which is the position of the second surface S2 corresponding to theposition of the quantum bit 4 included in the wiring pattern CP formedon the first surface S1, and supplies the control signal to the quantumbit 4.

With this configuration, in the superconducting complex quantumcomputing circuit QC according to the present embodiment, it is possibleto secure a constant density of the wiring pattern CP regardless of thenumber of quantum bits 4 on the substrate surface S of the circuitsubstrate 1. Therefore, it is possible to suppress an increase in thedensity of the wiring pattern CP on the substrate surface S of thecircuit substrate 1.

Conventionally, the control signal line is introduced from the sidesurface of the substrate and controls the quantum bits arranged on thetwo-dimensional plane of the surface of the substrate from the peripheryof the substrate. In a conventional circuit, as the number of quantumbits increases, the wiring density of the circuit increases, whicheventually reaches its limit.

On the other hand, in the superconducting complex quantum computingcircuit QC according to the present embodiment, a three-dimensionalstructure is made in which the control signal line 5 is arranged on thesecond surface S2 on the lower side of the circuit substrate 1 or thefirst surface S1 on the upper side. Therefore, it is possible to securethe constant density of the wiring pattern CP regardless of the numberof quantum bits 4. In the superconducting complex quantum computingcircuit QC according to the present embodiment, it is possible to securethe constant density of the wiring pattern CP regardless of the numberof quantum bits 4. Therefore, it is possible to ensure expandabilitytoward a large-scale circuit.

Further, in the superconducting complex quantum computing circuit QCaccording to the present embodiment, the frequency band of the controlsignal supplied to the quantum bit 4 through the control signal line 5is the microwave band.

In the superconducting complex quantum computing circuit QC according tothe present embodiment, it is possible to use a microwave signal for thecontrol and the observation. Therefore, as compared to the control byradio frequency (RF) according to the related art, it is possible tominimize a surface current area through which the ground electrodeflows, and it is possible to suppress fluctuation of an electrodepotential.

Modified Example of Metal Electrode Constituting Quantum Bit

In the above-described embodiment, the case where the inner disk 40,which is the metal electrode constituting the quantum bit 4, and theouter ring 41 form the concentric metal electrodes is described.However, a shape of the metal electrode constituting the quantum bit 4is not limited to the concentric circle.

Here, a modified example of the shape of the metal electrodeconstituting the quantum bit 4 will be described with reference to FIGS.12 to 18. In the modified example, parts different from the metalelectrode (FIG. 4) constituting the quantum bit 4 of the above-describedembodiment will be mainly described.

FIG. 12 is a diagram showing an example of a quantum bit 4 a accordingto the modified example of the present embodiment. The quantum bit 4 aincludes an inner disk 40 a, an outer ring 41 a, a Josephson junction 42a, a quantum bit hand portion 43 a-1, and a quantum bit hand portion 43a-2.

Unlike the outer ring 41 (FIG. 4), the outer ring 41 a is not closed andhas a gap 44 a.

FIG. 13 is a diagram showing an example of a quantum bit 4 b accordingto the modified example of the present embodiment. The quantum bit 4 bincludes an inner disk 40 b, an outer ring 41 b, a Josephson junction 42b, a quantum bit hand portion 43 b-1, and a quantum bit hand portion 43b-2.

Unlike the outer ring 41 (FIG. 4), the outer ring 41 b is not closed andhas a gap 44 b. Unlike the outer ring 41 a (FIG. 12), the outer ring 41b is not directly connected to the quantum bit hand portion 43 b.

The outer ring 41 b has a convex portion 45 b-1 and a convex portion 45b-2. The quantum bit hand portion 43 b-1 has a tip portion 46 b-1, andthe quantum bit hand portion 43 b-2 has a tip portion 46 b-2. The convexportion 45 b-1 and the convex portion 45 b-2 form concave portionsaccording to shapes of the tip portion 46 b-1 and a tip portion 46 b-2.

FIG. 14 is a diagram showing an example of a quantum bit 4 c accordingto the modified example of the present embodiment. The quantum bit 4 cincludes a first rectangle 40 c, a second rectangle 41 c, a Josephsonjunction 42 c, a quantum bit hand portion 43 c-1, and a quantum bit handportion 43 c-2

The first rectangle 40 c and the second rectangle 41 c are connected bythe Josephson junction 42 c. A distance between the first rectangle 40 cand a substrate top surface ground electrode 11 c-6 is large enough tomake the value of the first capacitance C1 sufficiently smaller than thevalue of the second capacitance C2. In FIG. 14, as an example, an areaof the first rectangle 40 c is reduced and the distance between thefirst rectangle 40 c and the substrate top surface ground electrode 11c-6 is increased. A length of a side of the second rectangle 41 c facingthe first rectangle 40 c is longer than a length of a side of the firstrectangle 40 c facing the second rectangle 41 c.

The quantum bit hand portion 43 c-1 and the quantum bit hand portion 43c-2 are not directly connected to the second rectangle 41 c.

Shapes of a substrate top surface ground electrode 11 c-5 and asubstrate top surface ground electrode 11 c-6 are different from thoseof the substrate top surface ground electrode 11-5 (FIG. 4) and thesubstrate top surface ground electrode 11-6 (FIG. 4) according to ashape of the first rectangle 40 c and a shape of the second rectangle 41c.

FIG. 15 is a diagram showing an example of a quantum bit 4 d accordingto the modified example of the present embodiment. The quantum bit 4 dincludes a first rectangle 40 d, a second rectangle 41 d, a Josephsonjunction 42 d, a quantum bit hand portion 43 d-1, and a quantum bit handportion 43 d-2

A distance between the first rectangle 40 d and the substrate topsurface ground electrode 11 d-6 is large enough to make the value of thefirst capacitance C1 sufficiently smaller than the value of the secondcapacitance C2. In FIG. 15, as an example, an area of the firstrectangle 40 d is reduced and the distance between the first rectangle40 d and the substrate top surface ground electrode 11 d-6 is increased.In the example shown in FIG. 15, a length of a side of the secondrectangle 41 d facing the first rectangle 40 d is equal to a length of aside of the first rectangle 40 d facing the second rectangle 41 d. Thelength of the side of the second rectangle 41 d facing the firstrectangle 40 d and the length of the side of the first rectangle 40 dfacing the second rectangle 41 d may not be equal as in the firstrectangle 40 c and the second rectangle 41 c in FIG. 14.

The quantum bit hand portion 43 d-1 has a bent tip portion 46 d-1, andthe quantum bit hand portion 43 d-2 has a bent tip portion 46 d-2. Asubstrate top surface ground electrode 11 d-5 has a convex portion 110d. The tip portion 46 d-1, the tip portion 46 d-2, and the convexportion 110 d face the second rectangle 41 d. In the quantum bit 4 d ofFIG. 15, due to the tip portion 46 d-1, the tip portion 46 d-2, and theconvex portion 110 d, the second capacitance C2 becomes large, comparedto the case where the tip portion 46 d-1, the tip portion 46 d-2, andthe convex portion 110 d are not provided.

FIG. 16 is a diagram showing an example of a quantum bit 4 e accordingto the modified example of the present embodiment. The quantum bit 4 eincludes a first rectangle 40 e, a cross 41 e, and a Josephson junction42 e. Each of a cross part 43 e-1 and a cross part 43 e-2 is shown as apart of a cross of a quantum bit adjacent to the quantum bit 4 e.

The first rectangle 40 e and the cross 41 e are connected by theJosephson junction 42 e.

Shapes of a substrate top surface ground electrode 11 e-5 and asubstrate top surface ground electrode 11 e-6 are different from thoseof the substrate top surface ground electrode 11-5 (FIG. 4) and thesubstrate top surface ground electrode 11-6 (FIG. 4) according to ashape of the first rectangle 40 e and a shape of the cross 41 e.

FIG. 17 is a diagram showing an example of a quantum bit 4 f accordingto the modified example of the present embodiment. The quantum bit 4 fincludes a first rectangle 40 f, a cross 41 f, and a Josephson junction42 f Each of a cross part 43 f-1 and a cross part 43 f-2 is shown as apart of a cross of a quantum bit adjacent to the quantum bit 4 f.

The quantum bit 4 f (FIG. 17) is different from the quantum bit 4 e(FIG. 16) in that a distance between the first rectangle 40 f (FIG. 17)and a substrate top surface ground electrode 11 f-2 (FIG. 17) is largerthan a distance between the first rectangle 40 e (FIG. 16) and asubstrate top surface ground electrode 11 e-2 (FIG. 16). In the example,the shape of the part of the substrate top surface ground electrode 11e-2 (FIG. 16) facing the cross 41 e (FIG. 16) and the first rectangle 40e (FIG. 16) is a straight line. In contrast, the shape of the part ofthe substrate top surface ground electrode 11 f-2 (FIG. 17) facing thecross 41 f (FIG. 17) and the first rectangle 40 f (FIG. 17) is a curvedline. Therefore, a distance between the first rectangle 40 f (FIG. 17)and the substrate top surface ground electrode 11 f-2 (FIG. 17) islarge.

In the quantum bit 4 f (FIG. 17), the distance between the firstrectangle 40 f (FIG. 17) and the substrate top surface ground electrode11 f-2 (FIG. 17) is large, so that the first capacitance C1 is smallerthan that of the quantum bit 4 e (FIG. 16).

FIG. 18 is a diagram showing an example of a quantum bit 4 g accordingto the modified example of the present embodiment. The quantum bit 4 gincludes a first electrode 40 g, a second electrode 41 g, a Josephsonjunction 42 g, a quantum bit hand portion 43 g-1, and a quantum bit handportion 43 g-2.

The first electrode 40 g and the second electrode 41 g are connected bythe Josephson junction 42 g. The first electrode 40 g and the secondelectrode 41 g each have a comb-shaped shape, and form a comb-shapedelectrode by facing each other. In the example shown in FIG. 18, thefirst electrode 40 g has two teeth and the second electrode 41 g hasthree teeth.

A distance between the first electrode 40 g and the substrate topsurface ground electrode 11 g-6 is large enough to make the value of thefirst capacitance C1 sufficiently smaller than the value of the secondcapacitance C2. In FIG. 18, as an example, an area of the firstelectrode 40 g is reduced and the distance between the first electrode40 g and the substrate top surface ground electrode 11 g-6 is increased.

In the above-described modified examples, the inner disk 40 a, the innerdisk 40 b, the first rectangle 40 c, the first rectangle 40 d, the firstrectangle 40 e, the first rectangle 40 f, and the first electrode 40 gare examples of the first electrode. The outer ring 41 a, the outer ring41 b, the second rectangle 41 c, the second rectangle 41 d, the cross 41e, the cross 41 f, and the second electrode 41 g are examples of thesecond electrode.

A coupling capacitance between the second electrode and the groundportion GE is larger than a coupling capacitance between the firstelectrode and the ground portion GE. A potential difference between thefirst electrode and the second electrode is hardly affected byfluctuation of the potential due to the unnecessary radiation electricfield E, compared to a case where the coupling capacitance between thesecond electrode and the ground portion GE is not larger than thecoupling capacitance between the first electrode and the ground portionGE.

Modified Example of Filter Pattern

In the above-described embodiment, the case where, in the filter pattern6, the central electrode 60 and the substrate bottom surface groundelectrode 13 are connected by the four connection electrodes 62 has beendescribed. However, the present invention is not limited thereto.

Here, modified examples of the filter pattern 6 will be described withreference to FIGS. 19 to 21. In the modified examples, parts differentfrom the filter pattern 6 (FIG. 6) of the above-described embodimentwill be mainly described.

FIG. 19 is a diagram showing an example of a filter pattern 6 aaccording to the present embodiment. The filter pattern 6 a includes acentral electrode 60 a and a connection electrode 62 a. The centralelectrode 60 a is surrounded by a substrate bottom surface groundelectrode 13 a via a gap portion 61 a. The central electrode 60 a andthe substrate bottom surface ground electrode 13 a are connected by oneconnection electrode 62 a.

The number of connection electrodes 62 is not limited to the case offour described in FIG. 6 or the case of one described in FIG. 19, andthe number of connection electrodes 62 may be two, three, five or more.

FIG. 20 is a diagram showing an example of a filter pattern 6 baccording to the present embodiment. The filter pattern 6 b includes acentral electrode 60 b and a connection electrode 62 b. The centralelectrode 60 b is surrounded by a substrate bottom surface groundelectrode 13 b via a gap portion 61 b. The central electrode 60 b andthe substrate bottom surface ground electrode 13 b are connected via theconnection electrode 62 b.

In the filter pattern 6 b, the central electrode 60 b and the connectionelectrode 62 b are integrally provided. The central electrode 60 b andthe connection electrode 62 b form a curved contour, as an example. Awidth of the connection electrode 62 b (FIG. 20) becomes narrow in adirection from the central electrode 60 b toward the substrate bottomsurface ground electrode 13 b.

The number of connection electrodes 62 b is not limited to the case ofone described in FIG. 20, and may be two or more.

FIG. 21 is a diagram showing an example of a filter pattern 6 caccording to the present embodiment. The filter pattern 6 c includes acentral electrode 60 c, a connection electrode 62 c-1, and a connectionelectrode 62 c-2. The central electrode 60 c is surrounded by asubstrate bottom surface ground electrode 13 c via a gap portion 61 b-1and a gap portion 61 b-2. The central electrode 60 c and the substratebottom surface ground electrode 13 c are connected via the connectionelectrode 62 c-1 and the connection electrode 62 c-2.

A shape of the central electrode 60 c is a rectangle.

The number of connection electrodes 62 c-1 and the number of connectionelectrodes 62 c-2 is not limited to the case of two described in FIG.21, and may be one or three or more.

Although some embodiments are described in detail with reference to thedrawings, a specific configuration is not limited to the abovedescription, and various design changes and the like are possible in ascope not departing from the gist of the invention.

REFERENCE NUMERALS LIST

-   -   QC: Superconducting complex quantum computing circuit    -   1: Circuit substrate    -   S: Substrate surface    -   S1: First surface    -   S2: Second surface    -   2: First ground electrode    -   3: Second ground electrode    -   4: Quantum bit    -   5: Control signal line    -   6: Filter pattern    -   7: Superconducting resonator    -   8: Observation electrode    -   9: Capacitor    -   10: Through-electrode    -   10, 11: Substrate top surface ground electrode    -   12: First extension portion    -   13: Substrate bottom surface ground electrode    -   14: Second extension portion    -   20: First non-contact portion    -   21: First contact portion    -   30: Second non-contact portion    -   31: Second contact portion    -   40: Inner disk    -   41: Outer ring    -   42: Josephson junction    -   43: Quantum bit hand portion    -   45: Substrate bottom surface ground electrode    -   46: tip portion    -   50: Contact pin    -   60: Central electrode    -   61: Gap portion    -   61, 62: Connection electrode    -   80: Observation substrate through-electrode    -   P: Pressing member    -   CP: Wiring pattern    -   GP: Ground pattern

1. A superconducting complex quantum computing circuit comprising: acircuit substrate in which a wiring pattern of a circuit element, whichincludes a plurality of quantum bits and a plurality of measurementelectrodes for observing a state of the quantum bit, and a plurality ofground pattern which are at a ground potential are formed on a substratesurface, and that includes a plurality of through-substrate electrodeswhich connect the ground pattern formed on a first surface of thesubstrate surface and the ground pattern formed on a second surface,which is a surface opposite the first surface, inside the substrate; afirst ground electrode that includes a first contact portion which is incontact with the ground pattern formed on the first surface of thecircuit substrate, and a first non-contact portion which has a shapecorresponding to a shape of the wiring pattern formed on the firstsurface; a second ground electrode that includes a second contactportion which is in contact with the ground pattern formed on the secondsurface of the circuit substrate; a plurality of control signal linesthat are provided with a contact spring pin at each tip, the pin beingin contact with a position corresponding to the quantum bit to press thefirst surface of the circuit substrate against the first groundelectrode or to press the second surface of the circuit substrateagainst the second ground electrode; and a pressing member that pressesthe first ground electrode against the first surface of the circuitsubstrate or presses the second ground electrode against the secondsurface of the circuit substrate, wherein the first ground electrode isin contact with the ground pattern via a first extension portion formedby a superconducting material having extensibility higher thanextensibility of the ground pattern, and the second ground electrode isin contact with the ground pattern via a second extension portion formedby a superconducting material having extensibility higher than theextensibility of the ground pattern.
 2. The superconducting complexquantum computing circuit according to claim 1, wherein the quantum bitincludes a first electrode that has a first coupling capacitance with aground portion, and a second electrode that has a second couplingcapacitance with a ground portion larger than the first couplingcapacitance and that is connected to the first electrode either by asingle Josephson junction or by a plurality of Josephson junctions. 3.The superconducting complex quantum computing circuit according to claim2, wherein the circuit substrate includes, at a quantum bitcorrespondence position, which is a position on the second surface,corresponding to a position of the quantum bit included in the wiringpattern formed on the first surface, a central electrode, a surroundingelectrode that surrounds the surroundings of the central electrode, anda single or a plurality of connection electrodes that connects thecentral electrode and the surrounding electrode.
 4. The superconductingcomplex quantum computing circuit according to any one of claims 1 to 3,wherein the control signal line is arranged inside the first non-contactportion included in the first ground electrode at a positioncorresponding to a position of the quantum bit included in the wiringpattern formed on the first surface or inside a second non-contactportion included in the second ground electrode at a positioncorresponding to a quantum bit correspondence position, which is aposition of the second surface corresponding to the position of thequantum bit included in the wiring pattern formed on the first surface,and supplies a control signal to the quantum bit.
 5. The superconductingcomplex quantum computing circuit according to claim 4, wherein thefirst non-contact portion and the second non-contact portion have awidth and a height with sizes smaller than a wavelength of the controlsignal.
 6. The superconducting complex quantum computing circuitaccording to claim 5, wherein a frequency band of the control signal isa microwave band.